This invention relates to improvements in tubes which are inserted into the body. More particularly, the invention involves the prevention of leakage from the vent lumen of a double-lumened nasograstric tube.
Nasogastric tubes are commonly used in hospitals and nursing homes to remove fluids from the stomach or to administer nutritives or medicines to a patient.
Nasogastric tubes are used, for example, postoperatively to prevent pooling of liquids in the stomach during recovery of the digestive function. They are also used in treatment of bleeding ulcers to remove blood from the stomach. They are also used for protecting gastric suture lines, for preventing and treating paralytic ileus, to decompress the stomach in circumstances which create outside pressure on the stomach, and in a host of other conditions.
The tube is conventionally a flexible plastic tube which is passed through the nasal canal, through the pharynx, and then down the esophagus into the stomach or small intestine. The lower or distal end of the tube in the stomach includes several openings or suction eyes to allow the passage of fluids.
When the tube is used for removing fluids from the stomach, the upper or proximal end of the tube is connected through a collector vessel to a vacuum pump system. Stomach fluids are drawn through the openings in the distal end of the tube, and into the collector vessel.
The openings in the distal end of the tube tend to become clogged. There are two major causes of such clogging. Debris in the stomach tends to be drawn into the openings. Further, as suction is applied to the nasogastric tube, the distal end of the tube drifts in the direction of the openings toward the wall of the stomach. Should the tube engage the wall of the stomach, occlusion of the openings may occur as the soft stomach lining (gastric mucosa) is drawn into the openings. Not only is the action of the tube blocked, but serious damage may be done to the wall of the stomach.
To help prevent blockage of the openings of a nasogastric tube, a double-lumened tube is generally used. The double lumened tube contains both a suction tube or lumen and a vent tube or lumen parallel to the suction lumen. Generally, both lumens are provided in a single tube, the vent lumen being a tube-within-a-tube. The vent lumen includes at least one small orifice into the suction lumen near their distal ends, to permit atmospheric air to be drawn through the vent lumen into the suction lumen.
A common commercially available double-lumened nasogastric tube is sold by Sherwood Medical Company under the trademark Salem Sump. The Salem Sump tube is formed as a tube-within-a-tube. The proximal end of the vent lumen is a pigtail about one foot long. The distal end of the vent lumen includes both an aperture into the suction lumen and a pair of openings into the stomach in its outer wall, on the side of the tube opposite the suction openings. The use and operation of the Salem Sump tube is described in an article by Edwina A. McConnell, in Nursing magazine, volume 7, number 9, September 1977, at pages 54-7, reprinted in Nursing 82.
When food or medication is passed down the suction lumen, the vent lumen is clamped or plugged, or air pressure is applied afterwards to clear the vent lumen. The present invention is primarily concerned with the functioning of a double-lumened nasogastric tube when suction is applied to the suction lumen.
During normal suctioning operation of the nasogastric tube, a small amount of atmospheric air is drawn through the vent lumen into the suction lumen at their distal ends, and is mixed with the stomach fluid as it is drawn from the stomach. During normal operation air bubbles will be visible in the stomach fluid as it passes through the tubing to the collector vessel. Should the suction tube openings become occluded, the presence of atmospheric air modifies the intensity of vacuum pressure spiking at the point of occlusion. Therefore, risk of damage to the stomach wall is reduced. Presence of atmospheric air at the point of occlusion also provides inducement for the tube to separate from the obstruction, thereby permitting the tube to resume normal operation.
The size of the orifice between the vent lumen and the suction lumen is chosen carefully to avoid interference with the normal operation of the suction lumen, and to diminish sudden spiking of vacuum pressure within the suction lumen should its openings become occluded. Other aspects of the system are also chosen carefully to balance efficiency of suctioning against the danger of occlusion. For example, either the suction on the pump is set to a low value, about 30-40 millimeters of mercury, or the pump is set to run intermittently (such as five seconds on and five seconds off at about 80-120 millimeters of mercury). These settings are selected so that the vacuum pressure at the suction openings is maintained below the level of capillary fragility, 25 millimeters of mercury. Should the stomach lining be drawn into the suction openings at a higher suction, serious damage to the lining can occur.
It will be seen that proper operation of the double lumen nasogastric tube depends on the continuous availability of atmospheric air to the suction openings through the aperture between the suction tube and the vent tube at their distal ends.
Unfortunately, double lumen nasogastric tubes frequently do not operate as intended. When stomach pressure is greater than atmospheric pressure, gastric reflux or leakage can occur, causing stomach fluids to escape through the vent lumen and out the pigtail onto the patient. Stomach pressure sufficient to cause gastric reflux is relatively common. It can be caused by as simple a force as coughing. It may also be caused, for example, by an overfilled stomach or by external pressure on the stomach caused by fluids in the abdominal cavity.
Reflux through the vent lumen of a double-lumened tube causes problems associated with the spillage of liquids through the pigtail and may also interfere with proper operation of the nasogastric tube.
The leakage of fluids due to gastric reflux can create severe medical problems. Stomach fluids are very acidic and will contribute to skin breakdown on contact. Leaking stomach or intestinal fluids can cause contamination of wounds, tubing and catheters. The leakage can be a source of hospital acquired (nosocomial) infections. Other medical problems can include inaccurate measurement of gastric secretions.
Spillage of stomach fluids causes further hospital problems. The burden of handling leakage or spills due to gastric reflux is usually the responsibility of the nursing staff. The recommended procedure is to wash the patient and change the patient's gown and bedliners following a period of leakage. Removal of equipment connections to the patient may also be required. This consumes a great deal of nursing time and adds to the cost of care. Unfortunately, the patient and bed are not always changed immediately following an episode of gastric reflux. Failure to change the patient may be the result of limited nursing resources or may be because the patient can not be removed from critical intravenous tubes, monitoring equipment or the like. The patient may thus be required to lie in the soiled bed for inordinate time periods, which causes patient discomfort, and may cause fear and additional medical problems.
Gastric reflux also may clog the vent lumen, either by drawing solid particles into the lumen or by drawing sufficient liquid into the vent lumen that the low or intermittent suction being applied to the suction lumen is insufficient to clear the vent lumen. Blockage of the vent lumen can lead to loss of function of the nasogastric tube and can result in stomach lesions and pooling of gastric fluids.
Gastric reflux has long been recognized as a problem with double-lumened nasogastric tubes. The generally recommended procedure for preventing reflux is to place the pigtail above the patient's midline, and to place the collection trap of the suction tube below the patient's midline. Unfortunately, the recommended placement of the tubes is not always practical, and even with such placement gastric reflux may occur. Maintaining the pigtail above the patient's midline generally involves pinning it to the patient's pillow, thereby severely limiting his or her head movement and adding significantly to discomfort. If the outlet of the vent tube is below the patient's midline (the approximate level of liquid in the patient's stomach), the vent tube can act as a siphon.
Nurses have developed a number of unorthodox techniques for precluding gastric reflux from the vent lumen of a double-lumened nasogastric tube. These include placing a stopper (such as a golf tee or a pencil tip) in the pigtail of the vent lumen, tying a surgical glove over the pigtail, or allowing the leakage to pool onto a napkin or into a receptacle. The first two methods defeat the function of the vent lumen. The third is tedious, further restricts patient movement, and frequently fails.